The Deadly Serious Challenge of Urban Heat & the Green Solutions Within Our Reach
It’s no surprise that Southern California is getting hotter. But higher temperatures paired with longer heat waves are especially dangerous for historically marginalized communities with substandard housing in park-poor neighborhoods with no trees. Where is the cooler, greener, shadier LA County that’s accessible to everyone?
Heat kills more Americans annually than all other climate disasters combined. And in a place like Los Angeles, there’s reason to believe the higher temperatures in store will be especially dangerous. By 2050, the number of dangerously hot days downtown LA will experience is expected to triple, taking a catastrophic toll on a city where our historically mild weather has left us utterly unprepared for 120 degree days. An aging population trapped in uninsulated apartments without air conditioning. Outdoor workers collapsing from heat exhaustion. Schools canceled due to blackouts. Asphalt that’s hot enough to send someone who touches it with their bare skin to the emergency room. Heat waves that dry brush to a crisp, increasing fire risk. Chronic dehydration and heat stress throughout an already vulnerable unsheltered population in a county where five homeless Angelenos die each day.
Even if greenhouse gas emissions are curbed per climate agreements to limit warming globally to 3.6 degrees (2 degrees Celsius), Southern California has already exceeded that dangerous threshold. Average regional temperatures for LA County have increased by 4.1 degrees since 1895, because urbanized areas warm at a faster rate than rural areas. This differential is due to the hardscape surfaces that absorb heat — buildings, parking lots, highways, and LA’s extra-wide streets — which create what’s known as an “urban heat island effect.” Not only does this drive temperatures higher during the day, the way those materials hold in heat prevent cities from cooling down at night. And if there are subsequent days of high temperatures without nighttime relief — like when a high pressure system known as a “heat dome” parks itself over LA — that higher overnight low temperature can make it impossible for the body to physically cool itself down.
Cooler temperatures are easier to find along the coast where ocean breezes and weather phenomena like June Gloom act like natural air conditioners. But these communities are also some of the most expensive in the region, largely because homeowners there often fight the construction of newer, denser housing. The search for more affordable rents forces families into hotter inland neighborhoods: by 2050, scientists believe residents of the San Gabriel Valley will experience 62 dangerously hot days per year while residents of Santa Monica will only be subjected to one. And for the most part, LA-area landlords are not legally required to provide air conditioning, although utility companies offer heavily subsidized window units for qualifying households, along with help paying bills which can skyrocket during summer months. (Even if they have AC, some low-income Angelenos don’t turn it on for fear of the excessive financial burden.) But unless cities work harder to lower their ambient temperatures, bringing more cooling units online will put increased stress on an already strained electrical grid — and, until those units are powered by 100 percent renewable energy, they’re just pumping more greenhouse gasses into an already warming atmosphere.
The challenge for LA is finding more ways to cool itself at the neighborhood scale. In recent years, city officials have allocated millions of climate mitigation dollars to a solution called cool pavement. This essentially entails painting LA’s hot asphalt streets with a white or light gray coat of slurry to reflect the sun’s rays, the same way that white- or light-painted roofs keep homes and buildings cooler. Although cool pavement does lower surface temperatures, research has shown that the reflection ends up making people using the street feel hotter. Painting pavement a lighter color also does nothing to address the core problem: LA still has way too much pavement. A better solution to cool down LA’s streets is much simpler and carries more benefits: planting trees.
Not only do trees create shade that prevent solar gain from heating up the pavement below, the evaporation of water from the leaves also cools the air around them. Neighborhoods with a healthy tree canopy can be 10 degrees cooler than a tree-less neighborhood, and streets where the urban canopy is close enough to touch overhead can be 20 to 45 degrees cooler than tree-less streets. (As an added bonus, these routes become more comfortable for people walking, biking, and waiting for buses.) Awnings, shade sails, and shade structures like bus shelters with accessible seating can serve as an adequate substitute. But the priority should be trees: they’re not just natural air conditioners — a young healthy tree has the net cooling power of 10 window AC units — they’re also air purifiers, biodiversity habitats, and carbon sequesters. It’s a win-win-win-win nature-based solution that also delivers additional physical and mental benefits. And it’s an ideal public health solution because cities can do targeted planting in communities where they know people are at risk for heat stress and respiratory illness. Healthy trees can reduce heat-related deaths by one-fifth.
But trees have unfortunately never been a priority for LA. In the 1970s, a utility manager for the city of Sacramento, which has a climate very similar to LA’s, proposed planting large shade trees as a way to save residents (and therefore the city) energy. Tree planting and maintenance efforts were funded like public infrastructure and now Sacramento has one of the densest urban forests in the world, with an average tree canopy of 23 percent. In comparison, about half of LA residents live in neighborhoods with tree canopies below 10 percent and the city’s canopy is so inequitably distributed that a quarter of all LA’s trees are located in just four neighborhoods (Pacific Palisades, Brentwood, Los Feliz and Shadow Hills). And in some cases, LA is also losing what little canopy it had: widened roads, increased development, slashed maintenance budgets, and years of drought means that many trees have been cut down or left to die. This rate of canopy loss is, unsurprisingly, higher in lower-income neighborhoods.
A tree audit has been conducted to target the areas of greatest need for planting. And the city is testing new climate-friendly species — not palm trees, which offer no shade at all — that will tolerate heat and drought without decimating sidewalks. But there’s still no comprehensive plan or funding for the neighborhoods that continue to swelter. The city claims it’s difficult to get permission from property owners of rental properties to plant on their parkways, which is why it relies more on voluntary planting by homeowners (who are more likely to live on better-shaded streets anyway). But planting trees can’t be an opt-in process; the loss of critical urban cooling infrastructure needs to be treated with the same urgency as a downed power line. LA County cities like Santa Monica and Pasadena offer a good model for prioritizing their urban canopies by treating trees like essential public amenities, planting larger and more mature trees in areas desperate for shading, and even making it more difficult for private property owners to cut mature trees down.
But just planting trees in all LA’s vacant tree wells isn’t enough to combat urban heat island effect. Much of the pavement surrounding those trees also needs to go. What cools down cities is permeable space: turning more pavement into parks. And, perhaps unsurprisingly, LA is among the most park-poor metropolitan areas in the U.S. According to an annual park equity survey by the Trust for Public Land, the city of LA ranks 80th out of 100 cities on park access. One-third of the city’s residents are more than a 10-minute walk to a park. Two-thirds of Angelenos live in what are considered to be park-poor neighborhoods. Besides providing access to shady trees, grassy knolls, and breezy waterways, an effectively designed and maintained park space can cool down a surrounding urban neighborhood by up to 6 degrees. And that park space can make a world of difference in an underserved neighborhood; it’s estimated that communities with household incomes of $60,000 or less are, on average, 5 degrees hotter than citywide averages.
LA has a yet-to-be unlocked tool that would lower temperatures and increase green space simultaneously: greening the nearly 1,000 mostly-blacktop schoolyards of the Los Angeles Unified School District. As the second-largest landowner in LA County, overseeing 6,400 acres, LAUSD properties are distributed fairly evenly across the county, and if these campuses were greened — meaning existing blacktop is mostly replaced with permeable pathways, shade trees, native plants, and some grass — it would guarantee daily healthy outdoor access to a half-million students every day. If these schoolyards were greened and also opened to the public through joint-use agreements, meaning community members could enjoy the grounds when school is not in session, the number of Angelenos within a 10-minute walk to a park would jump to 87.7 percent. LAUSD’s peer school districts across the country have comprehensive programs to both green and open schoolyards; LA is decades behind. This is clearly a top priority.
Outside of school properties, parks are largely created through what are known as “Quimby fees,” meaning developers of certain properties must either create park space or pay fees to create park space elsewhere. (A famous example is Grand Park in downtown LA, created when The Related Companies wanted to build a pair of towers on Grand Avenue; the park was funded and built a decade before the towers went in.) In 2016, LA’s City Council revised this process to ensure that the money for a park could be geographically reallocated to fund a park in a more disadvantaged community. Two measures passed the same year at the state and county level intended to further supplement those fees and address park inequities: Proposition 68, a bond for parks and watershed projects, and Measure A, an LA County parcel tax. LA County and LA City both have multiple, reliable funding resources for parks, including decades of investment in youth sports from the LA 84 Foundation, formed in the wake of the profit-generating 1984 Summer Olympics. Yet the city of LA’s stats are particularly dire: despite spending more per-capita on parks than it did a decade ago, LA’s park access rankings slipped from 65th in 2016 to 80th in 2023.
LA’s affordable housing crisis has also changed some park-creation rules for developers. Now, if developers agree to add more deed-restricted units for low-income residents, they can build more densely and remove certain tree-planting and on-site open space requirements. These incentives, while critical for building more housing, have decimated small-scale greening opportunities. LA needs to embrace a social housing model, where transit-accessible apartments are interwoven with park land, adding more units without requiring parking and without sacrificing open space. There doesn’t need to be a tradeoff between affordable housing and urban greening.
Besides, LA actually has plenty of room for more open space when its streets and sidewalks are seriously considered as greening opportunities. Our extra-wide roads have a lot of unused pavement, making them great candidates to be transformed into parklets and plazas. With a further reduction in car use, entire lanes can become greenways, linear parks, and bus rapid transit routes that move more people with fewer emissions. Across the county, 3 out of 4 bus shelters currently don’t have any shade, which will be essential to protect current riders from extreme heat. But adding shelters is the bare minimum — entire transit corridors need to be envisioned with shade in mind. Addressing heat in LA also means stopping highway expansions and road-widening projects that add more vehicles emitting smog-forming pollutants, making the air worse on hot days.
LA’s heat-combatting features of the future won’t look like the parks and tree wells of the past. Wet plazas, splash pads, and mist gardens will become infrastructural priorities. Microforests can cluster dozens of trees in a very small area to deliver shade relief and massive climate benefits. Dotting the region with hydration stations — another name for drinking fountains — and public restrooms will allow Angelenos to stay hydrated and healthy as they move around the city. Cooling centers are becoming “resilience hubs,” outfitted with solar panels in case the lights go out, which can serve as shelters on any day of the year. This kind of thinking underlines an important point about adapting to extreme heat. Existing heat mitigation efforts are largely couched within emergency departments to help vulnerable residents once it gets very hot. But LA must focus more heavily on prevention through bold, comprehensive infrastructural interventions that can give those same communities access to lower temperatures all year round. Instead of just thinking about extending hours at a lap pool or library once the thermometer hits 100, LA’s leaders need to instead be thinking more holistically about a city that naturally keeps itself cool for weeks on end — and where relief from that inevitable heat can be found on every corner.